Effect of Gd2O3 Addition on the Microstructure and Properties of Gd2O3-Yb2O3-Y2O3-ZrO2 (GYYZO) Ceramics

Gd and Yb elements have high chemical stability, which can stabilize the solid solution in ZrO₂. Gd₂O₃ and Yb₂O₃ have high melting points, and good oxidation resistance in extreme environments, stable chemical properties. Therefore, Gd₂O₃ and Yb₂O₃ were added to ZrO₂ to stabilize oxides, improve the high temperature stability, and effectively decrease the thermal conductivity at high temperature. In this work, 5 wt% Yb₂O₃ and 5 wt%, 10 wt%, 15 wt% Gd₂O₃ were doped into 8 wt% Y₂O₃ stabilized ZrO₂ (8YSZ) powders as thermal barrier coating materials, and sintered at 1650 °C for 6 h, 12 h, 24 h. The effects of Gd₂O₃ addition on the microstructure, density, thermal conductivity, hardness, and fracture toughness of Gd₂O₃-Yb₂O₃-Y₂O₃-ZrO₂ (GYYZO) bulk composite ceramics were investigated. It was found that the densification of the 8YSZ bulk and GYYZO bulk with 15 wt% Gd₂O₃ reached 96.89% and 96.22% sintered at 1650 °C for 24 h. With the increase of Gd₂O₃ addition, the hardness, elastic modulus and fracture toughness of the GYYZO bulk increased and the thermal conductivity and thermal expansion coefficient of the GYYZO bulk decreased. GYYZO bulk with 15 wt% Gd₂O₃ sintered at 1650 °C for 24h had the highest hardness, elastic modulus and fracture toughness of 15.61 GPa, 306.88 GPa, 7.822 MPa·m^0.5, and the lowest thermal conductivity and thermal expansion coefficient of 1.04 W/(m·k) and 7.89 × 10⁻⁶/°C at 1100 °C, respectively. The addition of Gd₂O₃ into YSZ could not only effectively reduce the thermal conductivity but also improve the mechanical properties, which would improve the thermal barrier coatings’ performances further.     

Enhancing the Oxidation Resistance of Al2O3-SiC-C Castables via Introducing Micronized Andalusite

Additions of andalusite aggregates (19 wt%) were shown in previous literature to enhance the antioxidation of Al₂O₃-SiC-C (ASC) castables. This work aims to investigate whether micronized andalusite has a greater influence on antioxidation improvement than andalusite aggregates. Various low contents (5 wt% and below) of micronized andalusite (≤5 μm) were introduced as a substitute for brown fused alumina in the matrix of ASC castables. The antioxidation of castable specimens was estimated by the oxidized area ratio on the fracture surface after a thermal shock test. The microstructure and phases of micronized andalusite and the castable specimens were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results suggest that the antioxidation effects of ASC castables with a low addition of micronized andalusite are effectively enhanced. The heat-induced transformation of andalusite produces SiO₂-rich glass, favoring the sintering of the castable matrix and impeding oxygen diffusion into the castable’s interior. Therefore, the castable antioxidation is enhanced without deteriorating the hot modulus of rupture.     

Recovery of Waste Polyurethane from E-Waste—Part I: Investigation of the Oil Sorption Potential

The shredding of end-of-life refrigerators produces every year in Italy 15,000 tons of waste polyurethane foam (PUF), usually destined for energy recovery. This work presents the results of the investigation of the oil sorption potential of waste PUF according to ASTM F726–17 standard. Three oils (diesel fuel and two commercial motor oils) having different densities (respectively, 0.83, 0.87, and 0.88 kg/dm³) and viscosities (respectively, 3, 95, and 140 mm²/s at 40 °C) were considered. The waste PUF was sampled in an Italian e-waste treatment plant, and its characterization showed 16.5 wt% particles below 0.71 mm and 13 wt% impurities (paper, plastic, aluminum foil), mostly having dimensions (d) above 5 mm. Sieving at 0.071 mm was applied to the waste PUF to obtain a “coarse” (d > 0.71 mm) and a “fine” fraction (d < 0.71 mm). Second sieving at 5 mm allowed an “intermediate” fraction to be obtained, with dimensions between 0.71 and 5 mm. The oil sorption tests involved the three fractions of waste PUF, and their performances were compared with two commercial oil sorbents (sepiolite and OKO-PUR). The results of the tests showed that the “fine” PUF was able to retain 7.1–10.3 g oil/g, the “intermediate” PUF, 4.2–7.4 g oil/g, and the “coarse” PUF, 4.5–7.0 g oil/g, while sepiolite and OKO-PUR performed worse (respectively, 1.3–1.6 and 3.3–5.3 g oil/g). In conclusion, compared with the actual management of waste PUF (100 wt% sent to energy recovery), the amount destined directly to energy recovery could be limited to 13 wt% (i.e., the impurities). The remaining 87 wt% could be diverted to reuse for oil sorption, and afterward directed to energy recovery, considered as a secondary option.     

Waste Originating from the Cleaning of Flue Gases from the Combustion of Industrial Wastes as a Lime Partial Replacement in Autoclaved Aerated Concrete

This paper aims to study the suitability of partial replacement of lime by waste originating from the cleaning of flue gases from the combustion of industrial wastes in the production of autoclaved aerated concrete (AAC). The compressive strength, bulk density, pore structure, phase composition, and microstructure of hydration products of the AAC were analyzed. According to the results, the addition of the waste can effectively enhance the mechanical properties of AAC due to the differences in morphology of hydration product—1.1 nm tobermorite and related dense microstructure. The pore size distribution was significantly influenced by waste addition, which was one of the main reasons for the increase in thermal conductivity. The XRD and SEM results showed that foreign ions introduced with the wastes affect the synthesis of 1.1 nm tobermorite. Moreover, it was shown that waste containing a high content of CaO can be used as lime replacement, which allows reducing CO₂ emissions during the AAC production process.     

Evaluation of Physical Properties of a Metakaolin-Based Alkali-Activated Binder Containing Waste Foam Glass

Foam glass production process redounds to large quantities of waste that, if not recycled, are stockpiled in the environment. In this work, increasing amounts of waste foam glass were used to produce metakaolin-based alkali-activated composites. Phase composition and morphology were investigated by means of X-ray powder diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy. Subsequently, the physical properties of the materials (density, porosity, thermal conductivity and mechanical strength) were determined. The analysis showed that waste foam glass functioned as an aggregate, introducing irregular voids in the matrix. The obtained composites were largely porous (>45%), with a thermal conductivity coefficient similar to that of timber (<0.2 W/m∙K). Optimum compressive strength was achieved for 10% incorporation of the waste by weight in the binder. The resulting mechanical properties suggest the suitability of the produced materials for use in thermal insulating applications where high load-bearing capacities are not required. Mechanical or chemical treatment of the waste is recommended for further exploitation of its potential in participating in the alkali activation process.     

Experimental Investigation on Mechanical and Thermal Properties of Concrete Using Waste Materials as an Aggregate Substitution

The continuous growth of the concrete industry requires an increased quantity of cement and natural aggregates year after year, and it is responsible for a major part of the global CO₂ emissions. These aspects led to rigorous research for suitable raw materials. Taking into account that these raw materials must have a sustainable character and also a low impact on environmental pollution, the replacement of the conventional components of concrete by residual waste can lead to these targets. This paper’s aim is to analyze the density, compressive strength and the thermal conductivity of nine concrete compositions with various rates of waste: four mixes with 10%, 20%, 40% and 60% chopped PET bottles aggregates and 10% fly ash as cement partial substitution; a mix with 60% waste polystyrene of 4–8 mm and 10% fly ash; a mix with 20% waste polystyrene of 4–8 mm, 10% waste polystyrene of 0–4 mm and 10% fly ash; a mix with 50% waste polystyrene of 4–8 mm, 20% waste polystyrene of 0–4 mm and 20% fly ash two mixes with 10% fly ash and 10% and 40% waste sawdust, respectively. Using 60% PET aggregates, 60% polystyrene granules of 4–8 mm, or 20% polystyrene of 0–4 mm together with 50% polystyrene of 4–8 mm led to the obtainment of lightweight concrete, with a density lower than 2000 kg/m³. These mixes also registered the best results from a thermal conductivity point of view, after the concrete mix with 40% saw dust. Regarding compressive strength, the mix with 10% PET obtained a result very close to the reference mix, while those with 20% PET, 40% PET, 30% polystyrene, and 10% saw dust, respectively, registered values between 22 MPa and 25 MPa, values appropriate for structural uses.     

Effect of Hollow Corundum Microspheres Additive on Physical and Mechanical Properties and Thermal Shock Resistance Behavior of Bauxite Based Refractory Castable

This paper analyses the effect of hollow corundum microspheres (HCM) on both physical-mechanical properties (density, ultrasonic pulse velocity, modulus of elasticity, and compressive strength) and thermal shock resistance behavior of refractory medium cement castable with bauxite aggregate. Moreover, the scanning electron microscopy (SEM) results of HCM and refractory castable samples are presented in the paper. It was found that the replacement of bauxite of 0–0.1 mm fraction by HCM (2.5%, 5%, and 10% by weight of dry mix) had no significant effect on the density and compressive strength of castable, while the modulus of elasticity decreased by 15%. Ultrasonic pulse velocity (Vup) values and the visual analysis of the samples after thermal cycling showed that a small amount of HCM in composition of refractory castable could reduce the formation and propagation of cracks and thus increase its thermal shock resistance.     

Borosilicate Glass-Ceramics Containing Zirconolite and Powellite for RE- and Mo-Rich Nuclear Waste Immobilization

In order to increase the loading of rare earth- and molybdenum-rich high-level waste in the waste forms, zirconolite- and powellite-based multi-phase borosilicate glass-ceramics were synthesized via an in-situ heat treatment method. The effects of the CTZ (CaO, TiO₂ and ZrO₂) content on the crystallization, microstructure and aqueous durability of the multi-phase borosilicate glass-ceramics were studied. The results indicate that the increase of CTZ content can promote crystallization. The glass-ceramics presented even structures when the CTZ content was ≥ 40 wt%. For the glass-ceramic with 40 wt% CTZ, only zirconolite and powellite crystals were detected and powellite crystals were mainly distributed around zirconolite, whereas for the glass-ceramics with 50 wt% CTZ, perovskite was detected. Furthermore, the leaching rates of Na, Ca, Mo and Nd were in the ×10⁻³, ×10⁻⁴, ×10⁻³ and ×10⁻⁵ g·m⁻²·d·⁻¹ orders of magnitude on the 28th leaching day, respectively.     

The Influence of Expanded Glass and Expanded Clay on Lightweight Aggregate Shotcrete Properties

In the construction industry, the selection of sustainable materials leads to a movement towards more sustainable construction. In this study, lightweight aggregate shotcrete based on expanded glass (EG) and expanded clay (EC) is investigated. The goal of the study is to determine the influence of EG and EC inclusion on the properties of shotcrete. Ordinary Portland cement (OPC) powder with supplementary cementitious materials, such as silica fume and ground glass waste, are used as binders. The mechanical, physical and morphological properties, as well as the mineral and oxygen compositions, are obtained through compressive and flexural strength tests, thermal conductivity measurements, scanning electron microscopy with energy dispersive X-ray spectrometry (SEM–EDX), X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis. In this study, the mechanical, physical and thermal properties and waste utilization as cement supplementary materials are balanced. The shotcrete samples show that a density of 790 kg/m³ had a good thermal performance (thermal conductivity coefficient of 0.174 W/(m·K)) with the sufficient compressive strength of 6.26 MPa.     

The Influence of Low-Temperature Food Waste Biochars on Anaerobic Digestion of Food Waste

The proof-of-the-concept of application of low-temperature food waste biochars for the anaerobic digestion (AD) of food waste (the same substrate) was tested. The concept assumes that residual heat from biogas utilization may be reused for biochar production. Four low-temperature biochars produced under two pyrolytic temperatures 300 °C and 400 °C and under atmospheric and 15 bars pressure with 60 min retention time were used. Additionally, the biochar produced during hydrothermal carbonization (HTC) was tested. The work studied the effect of a low biochar dose (0.05 g_BC × g_TSsubstrate⁻¹, or 0.65 g_BC × L⁻¹) on AD batch reactors’ performance. The biochemical methane potential test took 21 days, and the process kinetics using the first-order model were determined. The results showed that biochars obtained under 400 °C with atmospheric pressure and under HTC conditions improve methane yield by 3.6%. It has been revealed that thermochemical pressure influences the electrical conductivity of biochars. The biomethane was produced with a rate (k) of 0.24 d⁻¹, and the most effective biochars increased the biodegradability of food waste (FW) to 81% compared to variants without biochars (75%).     

Controlling the Thermal Stability of Kyanite-Based Refractory Geopolymers

The present project investigated the thermal stability of cold-setting refractory composites under high-temperature cycles. The proposed route dealt with the feasibility of using fillers with different particle sizes and studying their influence on the thermo-mechanical properties of refractory geopolymer composites. The volumetric shrinkage was studied with respect to particle sizes of fillers (80, 200 and 500 µm), treatment temperature (1050–1250 °C) and amount of fillers (70–85 wt.%). The results, combined with thermal analysis, indicated the efficiency of refractory-based kyanite aggregates for enhancing thermo-mechanical properties. At low temperatures, larger amounts of kyanite aggregates promoted mechanical strength development. Flexural strengths of 45, 42 and 40 MPa were obtained for geopolymer samples, respectively, at 1200 °C, made with filler particles sieved at 80, 200 and 500 µm. In addition, a sintering temperature equal to 1200 °C appeared beneficial for the promotion of densification as well as bonding between kyanite aggregates and the matrix, contributing to the reinforcement of the refractory geopolymer composites without any sign of vitrification. From the obtained properties of thermal stability, good densification and high strength, kyanite aggregates are efficient and promising candidates for the production of environmentally friendly, castable refractory composites.     

Research on the Preparation Parameters and Basic Properties of Premelted Calcium Aluminate Slag Prepared from Secondary Aluminum Dross

Secondary aluminum dross is a byproduct of the electrolytic aluminum industry, whose main components are Al₂O₃, AlN and Na₃AlF₆. Secondary aluminum dross is a type of hazardous waste, with a tremendous yield every year. Realizing the harmless treatment or resource utilization of secondary aluminum dross has important economic and social benefits. In the present research, the process of preparing premelted calcium aluminate slag used for molten steel refining from secondary aluminum dross was studied in detail. Firstly, the chemical composition and phase component of secondary aluminum dross were analyzed systematically. Then, according to phase diagram analysis and melting point measurement, the appropriate mixing ratio of CaO and secondary aluminum dross and the appropriate calcination temperature were determined. On this basis, an experiment of premelted calcium aluminate slag preparation was carried out in a tubular resistance furnace. The phase component and micromorphology of the premelted slag were analyzed by XRD and SEM. The results show that the main component of the premelted calcium aluminate slag is 11CaO·7Al₂O₃·CaF₂ phase with a low melting point. The original Na₃AlF₆ phase, which is the cause of leachable fluoride in secondary aluminum dross, disappears totally, and there is no water-soluble fluoride detected in the leaching toxicity detection. The research indicates that the process of preparing premelted calcium slag from secondary aluminum dross is feasible, which provides a helpful reference for the resource utilization of secondary aluminum dross.     

Characterization of Three Amu-Darya Basin Clays in Ceramic Brick Industry and Their Applications with Brick Waste

This study examined the chemical, mineralogical, physical, thermal, and technological characteristics of the Dostluk (DM), Halach (HM), and Sakar (HM) clay deposits located in the Amu-Darya basin of Turkmenistan. The potential suitability of these deposits was evaluated for the local ceramic brick industry. The chemical and mineralogical features were identified by X-ray fluorescence (XRF), ion chromatography (IC), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques. The physical properties were characterized by granulometric analysis by sieving, particle size distribution, scanning electron microscopy/optic analysis, specific surface area, Pfefferkon’s plasticity index, reabsorption, shrinkage, water absorption, mechanical (compression and bending), and freeze–thaw durability tests. The thermal methods were performed using dilatometry and thermogravimetric/differential thermal analyzer (TG/DTA). The test samples for the different clay deposits were extruded, dried, and fired at three different temperatures of 850 °C, 950 °C, and 1050 °C. While the Dostluk and Sakar clays have high plasticity, Halach clay has been found to have low plasticity. The mechanical and freeze–thaw durability tests demonstrated that the outcomes of the clays of different origins were sufficient, achieving compressive strengths of over 10 MPa and mass loss less than 3%, which are acceptable by industry standards. Semi-industrial processed hollow bricks demonstrated promising characteristics. While the Dostluk and Sakar clay-based brick specimens were visibly free of cracks, the Halach specimens showed some cracks. The physical and mechanical improvements of these clays were performed with three mixtures, which are M1 (80 mass% DM + 20 mass% brick waste), M2 (85 mass% SM + 15 mass% brick waste), and M3 (70 mass% HM + 25 mass% SM and 5 mass% brick waste) for the brick industry.     

Epoxy Composites Reinforced with ZnO from Waste Alkaline Batteries

The zinc alkaline battery is one of the most popular sources of portable electrical energy, with more than 300,000 tons being consumed per year. Accordingly, it is critical to recycle its components. In this work, we propose the use of zinc oxide (ZnO) microparticles recovered from worn-out batteries as fillers of epoxy resins. These nanocomposites can be used as protective coatings or pigments and as structural composites with high thermal stability. The addition of ceramic nanofillers, such as ZnO or/and TiO₂, could enhance the thermal and mechanical properties, and the hardness and hydrophobicity, of the epoxy resins, depending on several factors. Accordingly, different nanocomposites reinforced with recycled ZnO and commercial ZnO and TiO₂ nanoparticles have been manufactured with different nanofiller contents. In addition to the different ceramic oxides, the morphology and size of fillers are different. Recycled ZnO are“desert roses” such as microparticles, commercial ZnO are rectangular parallelepipeds nanoparticles, and commercial TiO₂ are smaller spherical nanoparticles. The addition of ceramic fillers produces a small increase of the glass transition temperature (<2%), together with an enhancement of the barrier effect of the epoxy resin, reducing the water diffusion coefficient (<21%), although the maximum water uptake remains constant. The nanocomposite water absorption is fully reversible by subsequent thermal treatment, recovering its initial thermomechanical behavior. The water angle contact (WCA) also increases (~12%) with the presence of ceramic particles, although the highest hydrophobicity (35%) is obtained when the epoxy resin reinforced with recycled flowerlike ZnO microparticles is etched with acid stearic and acetic acid, inducing the corrosion of the ZnO on the surface and therefore the increment of the surface roughness. The presence of desert rose ZnO particles enhances the de lotus effect.     

Impact of the Dopant Species on the Thermomechanical Material Properties of Thermoelectric Mg2Si0.3Sn0.7

Thermoelectric generators are an excellent option for waste heat reuse. Materials for such devices have seen their thermoelectric properties improving constantly. The functioning of a generator, however, does not only depend on thermoelectric properties. Thermal and mechanical properties play a decisive role in the feasibility of any thermoelectric generator. To shed light on the properties exhibited by thermoelectric materials, we present the temperature dependent characterization of Young’s modulus and coefficient of thermal expansion for Mg₂Si_0.3Sn_0.7. Comparing undoped to Bi-doped n-type and Li-doped p-type material, we investigated the influence of doping in the relevant temperature regime and found the influences to be minor, proving similar properties for n- and p-type. We found a Young’s modulus of 84 GPa for the p-type and 83 GPa for the n-type, similar to that of the undoped compound with 85 GPa. The thermal expansion coefficients of undoped, as well as n- and p-type were equally similar with values ranging from 16.5 to 17.5 × 10⁻⁶ 1/K. A phase analysis was performed to further compare the two materials, finding a similar phase distribution and microstructure. Finally, using the gathered data, estimations on the possible thermally induced stresses under a temperature difference are provided to evaluate the relevance of knowing temperature dependent thermal and mechanical properties.     

Preparation and Properties of Highly Elastic,Lightweight, and Thermally Insulating SiO2 Fibrous Porous Materials

Fibrous porous materials are one of the most commonly used high-temperature insulation materials because of their high porosity and low thermal conductivity. Due to their wide applications in the aerospace and energy industries, the investigation of high-elastic thermally insulating porous materials has attracted increasing attention. In order to improve the elasticity of fibrous porous materials, quartz fibers with high aspect ratio were used as matrix, sodium hexametaphosphate (SHMP) was selected as dispersant. We innovatively reported that a unique three-dimensional skeleton structure was constructed by adjusting the dispersion of fibers in the slurry, and the lightweight, thermal insulating and elastic SiO₂ fibrous porous material was then prepared by the compression molding method. The characterization results of zeta potential and absorbance showed that the addition of SHMP was an effective method to enhance the dispersibility of quartz fibers in the slurry. SiO₂ fibrous porous materials with 0.4 wt% SHMP content exhibited an ideal three-dimensional skeleton structure, which endowed the porous material with high porosity (89.39%), low density (0.04751 g/cm³), and low thermal conductivity (0.0356 W·m⁻¹·K⁻¹). The three-dimensional skeleton structure formed by overlapping fibers with high aspect ratios endowed the porous material with excellent elasticity. SiO₂ fibrous porous materials with 0.4 wt% SHMP content could undergo large strains of 30% and achieved a resilience ratio of 81.69% under the 30th compression cycle. Moreover, after heat treatment at 800 °C, SiO₂ fibrous porous materials also maintained good elasticity with a resilience ratio of more than 80%.     

Development of Y2O3 Dispersion-Strengthened Copper Alloy by Sol-Gel Method

In this study, oxide dispersion-strengthened Cu alloy with a Y₂O₃ content of 1 wt.% was fabricated through citric acid sol-gel synthesis and spark plasma sintering (SPS). The citric acid sol-gel method provides molecular mixing for the preparation of precursor powders, which produces nanoscale and uniformly distributed Y₂O₃ particles in an ultrafine-grained Cu matrix. The effects of nanoscale Y₂O₃ particles on the microstructure, mechanical properties and thermal conductivity of the Cu-1wt.%Y₂O₃ alloy were investigated. The average grain size of the Cu-1wt.%Y₂O₃ alloy is 0.42 μm, while the average particle size of Y₂O₃ is 16.4 nm. The unique microstructure provides excellent mechanical properties with a tensile strength of 572 MPa and a total elongation of 6.4%. After annealing at 800 °C for 1 h, the strength of the alloy does not decrease obviously, showing excellent thermal stability. The thermal conductivity of Cu-1wt.%Y₂O₃ alloy is about 308 Wm⁻¹K⁻¹ at room temperature and it decreases with increasing temperature. The refined grain size, high strength and excellent thermal stability of Cu-1wt.%Y₂O₃ alloys can be ascribed to the pinning effects of nanoscale Y₂O₃ particles dispersed in the Cu matrix. The Cu-Y₂O₃ alloys with high strength and high thermal conductivity have potential applications in high thermal load components of fusion reactors.     

Long-Term Leaching Behavior of Organic and Inorganic Pollutants after Wet Processing of Solid Waste Materials

The recycling of mineral materials is a sustainable and economical approach for reducing solid waste and saving primary resources. However, their reuse may pose potential risks of groundwater contamination, which may result from the leaching of organic and inorganic substances into water that percolates the solid waste. In this study, column leaching tests were used to investigate the short- and long-term leaching behavior of “salts”, “metals”, and organic pollutants such as PAHs and herbicides from different grain size fractions of construction & demolition waste (CDW) and railway ballast (RB) after a novel treatment process. Specifically, silt, sand and gravel fractions obtained after a sequential crushing, sieving, and washing process (“wet-processing”) of very heterogeneous input materials are compared with respect to residual contamination, potentially limiting their recycling. Concentrations in solid fractions and aqueous leachate were evaluated according to threshold values for groundwater protection to identify relevant substances and to classify materials obtained for recycling purposes according to limit values. For that, the upcoming German recycling degree was applied for the first time. Very good agreement was observed between short and extensive column tests, demonstrating that concentrations at L/S 2 ratios are suitable for quality control of recycling materials. Different solutes showed a characteristic leaching behavior such as the rapid decrease in “salts”, e.g., SO₄²⁻ and Cl⁻, from all solid fractions, and a slower decrease in metals and PAHs in the sand and silt fractions. Only the gravel fraction, however, showed concentrations of potential pollutants low enough for an unlimited re-use as recycling material in open technical applications. Sand fractions may only be re-used as recycling material in isolated or semi-isolated scenarios. Leaching from heterogeneous input materials proved harder to predict for all compounds. Overall, column leaching tests proved useful for (i) initial characterization of the mineral recycling materials, and (ii) continuous internal (factory control) and external quality control within the upcoming German recycling decree. Results from such studies may be used to optimize the treatment of mixed solid waste since they provide rapid insight in residual pollution of material fractions and their leaching behavior.     

Structural Analysis of Lignin-Based Furan Resin

The global “carbon emission peak” and “carbon neutrality” strategic goals promote us to replace current petroleum-based resin products with biomass-based resins. The use of technical lignins and hemicellulose-derived furfuryl alcohol in the production of biomass-based resins are among the most promising ways. Deep understanding of the resulting resin structure is a prerequisite for the optimization of biomass-based resins. Herein, a semiquantitative 2D HSQC NMR technique supplemented by the quantitative ³¹P NMR and methoxyl group wet chemistry analysis were employed for the structural elucidation of softwood kraft lignin-based furfuryl alcohol resin (LFA). The LFA was fractionated into water-insoluble (LFA-I) and soluble (LFA-S) parts. The analysis of methoxyl groups showed that the amount of lignin was 85 wt% and 44 wt% in LFA-I and LFA-S fractions, respectively. The HSQC spectra revealed the high diversity of linkages formed between lignin and poly FA (pFA). The HSQC and ³¹P results indicated the formation of new condensed structures, particularly at the 5-position of the aromatic ring. Esterification reactions between carboxyl groups of lignin and hydroxyl groups of pFA could also occur. Furthermore, it was suggested that lignin phenolic hydroxyl oxygen could attack an opened furan ring to form several aryl ethers structures. Therefore, the LFA resin was produced through crosslinking between lignin fragments and pFA chains.     

Recovery of Waste Polyurethane from E-Waste. Part II. Investigation of the Adsorption Potential for Wastewater Treatment

This study explored the performances of waste polyurethane foam (PUF) derived from the shredding of end-of-life refrigerators as an adsorbent for wastewater treatment. The waste PUF underwent a basic pre-treatment (e.g., sieving and washing) prior the adsorption tests. Three target pollutants were considered: methylene blue, phenol, and mercury. Adsorption batch tests were performed putting in contact waste PUF with aqueous solutions of the three pollutants at a solid/liquid ratio equal to 25 g/L. A commercial activated carbon (AC) was considered for comparison. The contact time necessary to reach the adsorption equilibrium was in the range of 60–140 min for waste PUF, while AC needed about 30 min. The results of the adsorption tests showed a better fit of the Freundlich isotherm model (R² = 0.93 for all pollutants) compared to the Langmuir model. The adsorption capacity of waste PUF was limited for methylene blue and mercury (K_f = 0.02), and much lower for phenol (K_f = 0.001). The removal efficiency achieved by waste PUF was lower (phenol 12% and methylene blue and mercury 37–38%) compared to AC (64–99%). The preliminary results obtained in this study can support the application of additional pre-treatments aimed to overcome the adsorption limits of the waste PUF, and it could be applied for “rough-cut” wastewater treatment.